CO reduction by calcium and ytterbium hydride complexes with a bulky monodentate carbazolyl ligand.

The bulky monodentate carbazolyl ligand 1,8-bis(3,5-ditertbutylphenyl)-3,6-ditertbutylcarbazole (dtbpCbz) was employed in the synthesis of monomeric heteroleptic amido carbazolyl complexes of Ca and Yb. For both central metal atoms, dimeric hydride complexes [(dtbpCbz)Ca(benzene)H]2, [(dtbpCbz)Ca(THF)H]2, [(dtbpCbz)Yb(benzene)H]2 and [(dtbpCbz)Yb(THF)H]2 were obtained, which show remarkably poor solubility in organic solvents. The characteristic hydride 1H NMR resonance of [(dtbpCbz)Ca(benzene)H]2 was observed at 2.07 ppm, and for the first time, characteristic vibrational modes of the Ca2H2 and Yb2H2 moiety are discussed. Despite their poor solubility, the hydride complexes could be reacted with CO to yield the corresponding ethenediolate complexes.